The present invention relates generally to the preparation of monolayered films for use in the microscopic examination of fluids. In particular, the invention is a portable device for uniformly smearing a cellular fluid on a microscope slide or the like without substantially altering the morphology of the components in the fluid.
It is estimated that the medical profession performs between 500 and 600 million venipunctures annually. The drawn blood samples are routinely examined by microscopy so that individual cells can be observed and abnormal cells identified. The cells, when distributed in a single layer on a slide and treated with a stain, can be counted to provide an index with which to diagnose the condition of the patient.
An elementary method of preparing a slide film for microscopic examinaton is to place a small quantity of a fluid, such as blood, on a slide. If a thin sample layer is desired, a second slide is placed over the first so that the fluid is dispersed between the two slides by drawing the slides together. The drawing action of this manual smear technique can produce an inconsistent distribution of cells with considerable cell overlapping and render a cell count imprecise. Cells may also be mechanically stretched and deformed, thus making a proper evaluation of cell morphology difficult.
Alternatively, the second slide can be held at an angle with respect to the first slide and drawn across the upper surface of the latter. A constant angle between the slides must be maintained during the drawing motion; the angle is critical to the smearing of a uniform film, but such precision is difficult to attain. As a result, smears produced by this method are often streaked and unevenly distributed.
Rather than drawing the slides together, the slides can be centrifuged to evenly distribute the fluid. In this manner, the mechanical deformation of cells is minimized. Centrifugation, however, requires expensive equipment and once the centrifuge apparatus is positioned and balanced, it cannot be moved conveniently so the technique must be performed at a single location.
Thus, the need exists for a device for preparing a fluid sample for microscopic examination wherein a uniform distribution of cells is achieved and cell deformation is minimized. It is also advantageous to have an inexpensive, portable device. The present and the copending applications are directed to the fulfillment of these needs.